Absorbent materials, especially granular absorbent materials, are used for a variety of industrial and household purposes. Typical uses include the absorption of liquids, such as water, oil, grease and solvents, spilled on floors and other surfaces, and as animal litters, such as cat litter.
Conventional granular liquid absorbents usually comprise naturally-occurring organic or inorganic absorbent materials, such as clay, sand, wood chips, sawdust, peanut shells, rice hulls and shredded paper, cardboard and newsprint. Animal litters comprise a special class of granular liquid absorbents and are used to collect animal waste products in households having pets, especially cats. Conventional animal litters typically comprise inert, high surface area materials, such as clay, bentonites and cellulose. Fragrances and odor-controlling agents can be added to some of these materials to improve and/or mask odors.
Conventional absorbent materials, including industrial-grade waste liquid absorbents and animal litters, are disadvantageous in that they generally have low absorbency, and suffer from dusting and disposal problems. Typical prior art absorbent materials can absorb an amount of liquid equal to or less than their own weight. Accordingly, these materials become saturated quickly and must be discarded and replaced frequently. This increases the costs associated with using industrial-grade waste liquid absorbents and animal litters. With particular reference to animal litters, there are also disposal problems since the saturated litters often cling to litter trays and pans. Conventional absorbents also possess high bulk densities, generally from about 36 to about 50 lbs/ft.sup.3, which creates handling problems for consumers. Conventional litters also tend to adhere to the feet of domestic pets, resulting in the litter being scattered out of the litter box. This creates housekeeping problems. Inorganic absorbents, such as clay absorbents, are also abrasive, and can cause damage to nearby flooring.
There is an increasing need for methods of disposal of fibrous sludge from paper processing plants. In a conventional paper deinking plant, 100 dry tons of waste paper can be processed into about 65 to about 80 dry tons of recycled (reusable) fiber. The remaining 20 to 35 tons of waste paper is unusable, and becomes part of the sludge produced by the deinking plant. This unusable sludge typically contains about 50 to about 70 percent water. Thus, 100 dry tons of waste paper can produce from about 70 to about 120 wet tons of sludge requiring disposal.
Conventional methods for disposing sludge include landfill disposal, land spreading, composting and incineration. Landfill and land spreading sites are being depleted at an alarming rate, and the establishment of new sites is difficult due to environmental concerns. Composting and incineration of sludge also raises environmental concerns. Some innovative sludge disposal techniques include processing the sludge into pellets for fuel or into lightweight aggregates for construction, pyrolysis, gasification, and incorporation into cements. However, these techniques generally require the use of complex methods and expensive equipment.
The incorporation of fiber sludge into animal litters has also been reported. For example, Lowe et al., U.S. Pat. No. 4,721,059 describes animal fillers produced from the waste material obtained during paper manufacture. The methods for making the animal fillers of Lowe et al. suffer from drawbacks in that they require that dewatered fibers be broken down or shredded with a delumper, reduction mill or shredder to a fiber length of 1 to 10 mm, with a fiber length of 1 to 4 mm being preferred. Breaking down or shredding the fibers to a specific fiber length requires additional manufacturing steps and, therefore, increased manufacturing costs.
Cortigene et al., U.S. Pat. No. 4,203,388 describes an animal litter comprising pelleted and dried rejects of a secondary fiber plant. The methods for making animal litters of Cortigene et al. suffer from drawbacks in that they require that the sludge be dewatered to a water content between about 32 and 40%. Dewatering sludge to a water content of 40% and below can be difficult. Moreover, the methods disclosed in the Cortigene et al. patent require that the dewatered sludge cake be cut into small pieces, prior to pelletizing. Dewatering the sludge to a water content of 40% or less and cutting the sludge cake into small pieces requires additional manufacturing steps and, therefore, increased manufacturing costs.
Although processes have been developed for recycling fiber sludge into recycled paper products, these processes have not been widely accepted because of the difficulty associated with controlling the quality of the resulting recycled paper products.
Accordingly, new and/or better absorbent materials, including absorbent materials for use as industrial-grade waste liquid absorbents and household absorbents, such as animal litters, are needed. In addition, new and/or better methods for the use or disposal of fibrous sludge are needed. The present invention is directed to these, as well as other important ends.